Kids today... they're not having as much sex as you might think. According to the largest and most detailed federal report ever on sexual activity in America, 29 percent of young women and 27 percent of young men ages 15 to 24 have never had a sexual encounter, a marked increase since the last survey was conducted in 2002. When it comes to sex, "there is a trend toward postponement," says Debbie Roffman, a human sexuality educator, as quoted in USA Today. Why are more teens waiting to have sex? Here, five theories:

1. Virginity is trendy
These findings just show that virginity isn't necessarily uncool, says Vanessa Ho in the Seattle Post Intelligencer. "Virginity is hot," and it's "been the new 'new' for a while, with a lot more talk of abstinence among teens and non-marrieds."

2. Sex education is working
Sex among unmarried adolescents began declining in 1988, too long ago to credit abstinence-only sex education pushed under President George W. Bush. Still, it's possible Bush's programs helped contribute to the decline, says Bill Albert, of the National Campaign to Prevent Teen and Unplanned Pregnancy, as quoted by the AP.

3. Teens have no time for nookie
Maybe kids today are "just too busy" for sex, say Carla K. Johnson and Mike Stobbe of the AP. "It's not even on my radar," says one 17-year-old, who starts her day at 5 a.m. and doesn't turn in until 10:30 p.m., packing her schedule with competitive swimming, schoolwork, running, weight training, and volunteering with service dogs and the disabled.

4. Youngsters want quality, not quantity
"More young people may be choosing to wait for a more quality sexual experience, knowing it is more likely to come with maturity," says Roffman, as quoted in USA Today.

5. Or maybe they just were not being honest

It's possible that all the young people surveyed weren't totally truthful about their sexual experience, and that's why we've seen the virginity spike, says psychologist Michael Bradley, as quoted in USA Today. "There is some awareness of confidentiality concerns among a lot of kids," and "we do see kids less inclined to disclose these things than in the past."